Field of the Invention
The present invention relates to a novel optically active substance and a liquid crystal composition comprising this optically active substance.
The liquid crystals currently widely used in a liquid crystal display (LCD) are classified into the nematic phase, and since they are of the light-receiving type, the display system using these liquid crystals is characterized in that there is no eye fatigue therefrom and the power consumption is very low. Nevertheless, the display system using these liquid crystals has problems in that the response speed is low and the view angle of the display is narrow.
A display device or printer head using a ferroelectric liquid crystal having advantageous characteristics inherently possessed by nematic liquid crystals, such as no eye-fatigue property and very low power consumption, and having high response speed and high contrast comparable to those of display elements of the light-emitting type, has been investigated.
The ferroelectric liquid crystal was discovered for the first time by R. B. Meyer et al in 1975 [J. physique, 36, L-69 (1975)]. This ferroelectric liquid crystal is classified into the chiral smectic C phase (hereinafter referred to as "Sm*C phase"), and a typical compound of this ferroelectric liquid crystal is p-decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (hereinafter referred to as "DOBAMBC") represented by the following formula: ##STR3##
DOBAMBC and most of the ferroelectric liquid crystal materials proposed thereafter, have problems in that the temperature range showing the ferroelectricity (the temperature range in which the Sm*C phase is present) is narrow, and they cannot be used practically without an additive. Accordingly, attempts have been made to expand the temperature range showing the Sm*C phase of the lower and higher temperature sides, taking room temperature as the center, by mixing ferroelectric liquid crystals each other or with other liquid crystals. Under this circumstance, the development of a ferroelectric liquid crystal showing the Sm*C phase in the practical temperature range is desired. Furthermore, the development of a ferroelectric liquid crystal having a larger spontaneous polarization than those of the known ferroelectric liquid crystals is desired in the field of printer heads for which an ultra-high response speed is required.
When ferroelectric liquid crystals having the Sm*C phase are mixed, the kinds of applicable compounds (liquid crystals) are limited, and liquid crystal mixtures which give satisfactory various performances are difficult to obtain at present. Compounds having a Schiff base, such as DOBAMBC, have a poor light stability and a coloration thereof readily occurs.